No Government License Rights
1. Field of the Invention
The present invention generally relates to a manufacturing method and resultant structure in the field of optical fibers. The invention specifically describes a method to chemically mill a fiber end and the resultant structure consisting of a lens and an attachment structure milled onto the fiber end.
2. Background of the Invention
The performance of optical fibers is critical to the telecommunications industry. Light energy loss is one of the most important parameters for defining fiber performance. Losses occur as light is attenuated while propagating through and exiting from a fiber.
Losses are both intrinsic and extrinsic. Intrinsic losses are caused by the absorption and scattering of light energy within a fiber. Such losses are minimized by core and cladding design. For example, losses as little as 0.4 decibels per kilometer are typical within commercially available single-mode fibers transmitting light at 1550 nanometer wavelength. Extrinsic losses result from back reflections of light at interfaces and misalignment between fiber and other components, such as detectors, light sources, and other fibers. Extrinsic losses are minimized by modifying the fiber end and improving alignment of such fibers with other components. Extrinsic losses are greater than intrinsic, therefore solutions minimizing the former provide significant performance advantages in telecommunication systems.
The related arts provide several methods and devices to minimize extrinsic losses. For example, a lens may be attached to or formed onto a fiber end to focus light. Whereas, precision alignment techniques maximize light energy coupled into neighboring components.
A chemical etch technique for forming a lens is described in the related arts. Bonham, et al., in U.S. Pat. No. 5,598,493, claims a chemical etch method of forming a lens onto an end of an optical fiber and describes a system to controllably insert and remove a fiber within an acid bath thereby achieving the desired lens shape. FIG. 1 graphically describes the Bonham method. An optical fiber 1 is inserted through an oil bath 2 into an acid bath 3, as shown in FIG. 1A. The optical fiber 1 is positioned so that a predetermined length resides within the acid bath 3 allowing the acid to etch the optical fiber 1. The acid completely etches the optical fiber 1 within the acid bath 3 and partially etches the optical fiber 1 within the oil bath 2, as shown in FIG. 1B. Thereafter, the taper 5 is controllably inserted into the acid bath 3 allowing for further etching of the fiber tip 15 along the acid-oil interface 10, as shown in FIG. 1C. The etch process progresses until a rounded end 6 is formed, as shown in FIG. 1D.
Bonham, et. al. is technically complex in terms of method and equipment. The described method achieves a tapered lens by precisely moving an optical fiber through an acid-oil interface in a multi-step progression. The precise positioning of fiber relative to acid-oil interface requires specialized computer-controlled manufacturing equipment with precision movement capability and software to control movement. Such complexities increase manufacturing costs and limit production yield. Furthermore, Bonham""s dependence on the interaction between acid-oil interface and terminal end precludes the controlled etching of fiber beyond the terminal end.
While the coupling end of a component is dimensionally precise, the fiber end attached at such coupling is not. The related arts have sought to address precision alignment between fibers and components by devices and methods separate and distinct from fiber structure.
Currently, optical fibers are precisely aligned by either passive or active means. Lee, et. al., in U.S. Pat. No. 6,118,917, describes a passive device for aligning one or more fibers by positioning an input fiber and an output fiber within a precision grove in two separate blocks and connecting said blocks to a precision coupler block with integral optical waveguide. Lee is an adaptation of the v-groove coupler known within the art. Lee""s invention, like other passive devices, provides precision alignment via dimensionally precise components. Proper alignment is merely achieved by attaching a fiber to a device. However, passive alignment devices are not compatible with many optical fiber applications due to size and geometric constraints.
Active alignment is generally a method consisting of positioning and adjusting an optical fiber relative to a mating component until the measured optical power at the other end of the coupling is at least the desired value. Haake, in U.S. Pat. No. 5,606,635, specifically describes an alignment method in which a miniature electrical device aligns one or more optical fibers. Fiber position is adjusted by applying a current to an electrostrictive or piezoelectric material that moves and deflects a fiber. While active alignment methods and devices optimize light energy coupling, they are costly and time consuming.
The related arts clearly demonstrate the limits of existing chemical etch methods as well as alignment methods and devices. What is currently required is a chemical mill method that addresses both focusing and alignment challenges. The method should form a lens onto a fiber end in a simple yet controllable fashion. Furthermore, the method should form a dimensionally precise region adjacent to the fiber end for alignment purposes. The milled fiber should both focus and align light entering or exiting the fiber.
The current invention provides for the controlled chemical mill of core and cladding of a fiber thereby forming both lens for focusing light and uniform diameter structure facilitating precision alignment of fiber with other components.
The disclosed method provides several advantages over existing methods. First, the method is both simple and reproducible thereby eliminating specialized equipment. Second, the method utilizes a low concentration acid thereby improving surface smoothness along the lens which in turn reduces light scatter and increases coupling efficiency. Third, the method provides a wide range of lens structures that alone or in combination with other lens structures better focuses light entering and exiting an optical fiber. Fourth, the alignment structure provides for a self-aligning fiber. Fifth, the combination lensed fiber with alignment structure provides for greater coupling of light energy into other components.
It is therefore an object of the present invention to avoid the disadvantages of the related art. More particularly, it is the object of the invention to provide a chemical mill method to simultaneously form both lens and alignment structure onto an optical fiber. It is also an object of the invention to provide a method to form such lens and alignment structure by statically positioning an optical fiber within an acid bath. It is also an object of the invention to provide a chemical milling method capable of forming a wide variety of lens shapes, examples including curved, frustum, and conical shaped lenses. It is also an object of the invention to provide a fiber end with conical lens and alignment structure. It is also an object of the invention to provide a fiber end with frustum shaped lens and alignment structure. It is also an object of the invention to provide a fiber end with frustum shaped lens onto which a second lens is attached. It is also an object of the invention to provide a method to form a wedge shaped lens.